Access to incorrect hostname needs error re: cross-domain

[julianlam]

If a NodeBB is set up with a certain base_url, and accessed via another base_url (that still points to the same machine), NodeBB loads but all calls to retrieve template data fail, as it is a cross-domain XHR.

The template engine needs a .fail() added on to throw a modal notifying the user that they're accessing the incorrect url, and provide a link to the actual URL.

This is a band-aid solution, there may be a way to resolve this problem altogether

Re: issues #355, #342, others.

[julianlam]

Scratch all of this, fix incoming.